Method for mapping physical hybrid automatic repeat request indicator channel

ABSTRACT

A method for mapping a physical hybrid automatic repeat request indicator channel (PHICH) is described. The method for mapping a PHICH includes determining an index of a resource element group transmitting a repetitive pattern of the PHICH, according to a ratio of the number of available resource element groups in a symbol in which the PHICH is transmitted and the number of available resource element groups in a first or second OFDM symbol, and mapping the PHICH to the symbol according to the determined index. In transmitting the PHICH, since efficient mapping is performed considering available resource elements varying with OFDM symbols, repetition of the PHICH does not generate interference between neighbor cell IDs and performance is improved.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 13/012,702, filed on Jan. 24, 2011, which is a continuation ofU.S. patent application Ser. No. 12/388,243, filed on Feb. 18, 2009, nowissued as U.S. Pat. No. 7,894,330, all of which claim priority from andthe benefit of U.S. Provisional Application Ser. No. 61/029,895, filedon Feb. 19, 2008, and Korean Patent Application No. 10-2008-0124084,filed on Dec. 8, 2008, which are all hereby incorporated by referencefor all purposes as if fully set forth herein.

BACKGROUND

1. Field

The present invention relates to a mapping method for frequency andorthogonal is frequency division multiplexing (OFDM) symbol regions of asignal transmitted on downlink in a cellular OFDM wireless packetcommunication system.

2. Discussion of the Background

When transmitting/receiving a packet in a mobile communication system, areceiver should inform a transmitter as to whether or not the packet hasbeen successfully received. If the reception of the packet issuccessful, the receiver transmits an acknowledgement (ACK) to cause thetransmitter to transmit a new packet. If the reception of the packetfails, the receiver transmits a negative acknowledgement (NACK) to causethe transmitter to re-transmit the packet. Such a process is calledautomatic repeat request (ARQ). Meanwhile, hybrid ARQ (HARQ), which is acombination of the ARQ operation and a channel coding scheme, has beenproposed. HARQ lowers an error rate by combining a re-transmitted packetwith a previously received packet and improves overall systemefficiency. In order to increase throughput of the system, HARQ demandsa rapid ACK/NACK response from the receiver compared with a conventionalARQ operation. Therefore, the ACK/NACK response in HARQ is transmittedby a physical channel signaling method. The HARQ scheme may be broadlyclassified into chase combining (CC) and incremental redundancy (IR).The CC method serves to re-transmit a packet using the same modulationmethod and the same coding rate as those used when transmitting aprevious packet. The IR method serves to re-transmit a packet using adifferent modulation method and a different coding rate from those usedwhen transmitting a previous packet. In this case, the receiver canraise system performance through coding diversity.

In a multi-carrier cellular mobile communication system, mobile stationsbelonging to one or a plurality of cells transmit an uplink data packetto a base station. That is, since a plurality of mobile stations withinone sub-frame can transmit an uplink data packet, the base station mustbe able to transmit ACK/NACK signals to a plurality of mobile stationswithin one sub-frame. If the base station multiplexes a plurality ofACK/NACK signals transmitted to the mobile stations within one sub-frameusing CDMA scheme within a partial time-frequency region of a downlinktransmission band of the multi-carrier system, ACK/NACK signals withrespect to other mobile stations are discriminated by an orthogonal codeor a quasi-orthogonal code multiplied through a time-frequency region.If quadrature phase shift keying (QPSK) transmission is performed, theACK/NACK signals may be discriminated by different orthogonal phasecomponents.

When transmitting the ACK/NACK signals using CDMA multiplexing scheme inorder to transmit a plurality of ACK/NACK signals within one sub-frame,a downlink wireless channel response characteristic should not begreatly varied in a time-frequency region in which the ACK/NACK signalsare transmitted. This is because if orthogonality is maintained betweenthe multiplexed different ACK/NACK signals, a receiver can obtainsatisfactory reception performance without applying a special receivingalgorithm such as channel equalization. Accordingly, the CDMAmultiplexing of the ACK/NACK signals should be performed within thetime-frequency region in which a wireless channel response is notsignificantly varied. However, if the wireless channel quality of aspecific mobile station is poor in the time-frequency region in whichthe ACK/NACK signals are transmitted, the ACK/NACK reception performanceof the mobile station may also be greatly lowered.

Accordingly, the ACK/NACK signals transmitted to any mobile stationwithin one sub-frame may be repeatedly transmitted over separatetime-frequency regions in a plurality of time-frequency axes, and theACK/NACK signals may be multiplexed with ACK/NACK signals transmitted toother mobile stations by CDMA in each time-frequency region. Therefore,the receiver can obtain a time-frequency diversity gain when receivingthe ACK/NACK signals.

However, in a conventional physical hybrid ARQ indicator channel (PHICH)mapping method, there exists a defect that PHICH groups between neighborcells have difficulty avoiding collision as illustrated in FIG. 1.

SUMMARY

An object of the present invention devised to solve the problem lies inproviding a method for mapping a PHICH so that repetition of the PHICHdoes not generate interference between neighbor cell IDs by consideringavailable resource elements varying with OFDM symbols.

The object of the present invention can be achieved by providing amethod for mapping a PHICH, including determining an index of an OFDMsymbol in which a PHICH group is transmitted, determining an index of aresource element group transmitting a repetitive pattern of the PHICHgroup, according to a ratio of the number of available resource elementgroups in the determined OFDM symbol and the number of availableresource element groups in a first or second OFDM symbol, and mappingthe PHICH group according to the determined index.

The PHICH may be transmitted in units of a plurality of PHICH groups,and an index of an OFDM symbol in which an i-th repetitive pattern istransmitted may be defined by the following equation:

$l_{i}^{\prime} = \left\{ \begin{matrix}0 & \begin{matrix}{{{normal}\mspace{14mu} {PHICH}\mspace{14mu} {duration}},} \\{{all}\mspace{14mu} {subframes}}\end{matrix} \\i & \begin{matrix}{{{extended}\mspace{14mu} {PHICH}\mspace{14mu} {duration}},} \\{{non}\text{-}{MBSFN}\mspace{14mu} {subframes}}\end{matrix} \\{\left( {\left\lfloor {m^{\prime}/2} \right\rfloor + i + 1} \right){mod}\; 2} & \begin{matrix}{{{extended}\mspace{14mu} {PHICH}\mspace{14mu} {duration}},} \\{{MBSFN}\mspace{14mu} {subframes}}\end{matrix}\end{matrix} \right.$

where m′ denotes an index of a PHICH group

The index of the resource element group may be determined according to avalue obtained by multiplying the ratio by a cell ID.

The index of the resource element group may be determined by thefollowing equation:

${\overset{\_}{n}}_{i} = \left\{ \begin{matrix}{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{0}^{\prime}}} \right) \right\rfloor + m^{\prime}} \right)\mspace{14mu} {mod}\mspace{14mu} n_{l_{i}^{\prime}}^{\prime}},} & {i = 0} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{0}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {n_{l_{i}^{\prime}}^{\prime}/3} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 1} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{0}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {2\; {n_{l_{i}^{\prime}}^{\prime}/3}} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 2}\end{matrix} \right.$

where N_(ID) ^(cell) denotes a cell ID, i denotes an index of arepetitive pattern, n′_(l′) _(i) /n′₀ denotes a ratio between the numberof available resource element groups in an OFDM symbol l′_(i) and thenumber of available resource element groups in a first OFDM symbol, andm′ denotes an index of a PHICH group.

In accordance with another aspect of the present invention, there isprovided a method for mapping a PHICH, including determining an index ofa resource element group transmitting a repetitive pattern of the PHICH,according to a ratio of the number of available resource element groupsin a symbol in which the PHICH is transmitted and the number ofavailable resource element groups in a second OFDM symbol, and mappingthe PHICH to the symbol according to the determined index.

The PHICH may be transmitted in units of a plurality of PHICH groupseach consisting of four resource elements.

The PHICH may be transmitted in units of a plurality of PHICH groupseach consisting of two resource elements.

The index of the resource element group may be determined by thefollowing equation:

${\overset{\_}{n}}_{i} = \left\{ \begin{matrix}{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{1}^{\prime}}} \right) \right\rfloor + m^{\prime}} \right)\mspace{14mu} {mod}\mspace{14mu} n_{l_{i}^{\prime}}^{\prime}},} & {i = 0} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{1}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {n_{l_{i}^{\prime}}^{\prime}/3} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 1} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{1}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {2\; {n_{l_{i}^{\prime}}^{\prime}/3}} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 2}\end{matrix} \right.$

where N_(ID) ^(cell) denotes a cell ID, i denotes an index of arepetitive pattern, n′_(l′) _(i) /n′₁ denotes a ratio between the numberof available resource element groups in an OFDM symbol l′_(i) and thenumber of available resource element groups in a second OFDM symbol, andm′ denotes an index of a PHICH group.

According to the exemplary embodiment of the present invention,efficiency mapping is performed by considering available resourceelements varying according to OFDM symbols during PHICH transmission, sothat PHICH repetition does not generate interference between neighborcell IDs and performance is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention.

In the drawings:

FIG. 1 illustrates an example of a conventional PHICH mapping method;

FIGS. 2 and 3 illustrate resource element groups to which a PHICH ismapped;

FIGS. 4 and 5 illustrate examples of mapping a PHICH when a spreadingfactor is 4;

FIGS. 6 and 7 illustrate examples of mapping a PHICH when a spreadingfactor is 2;

FIGS. 8 to 10 illustrate examples of repetitive mapping of a PHICHapplied to the present invention; and

FIG. 11 illustrates an example of a PHICH mapping method according to anexemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to the exemplary embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The detailed description, which will be given below withreference to the accompanying drawings, is intended to explain exemplaryembodiments of the present invention, rather than to show the onlyembodiments that can be implemented according to the invention.

When transmitting data through downlink of an OFDM wireless packetcommunication system, a channel transmitting ACK/NACK signals may bereferred to as a physical hybrid ARQ indicator channel (PHICH).

In a 3^(rd) generation partnership project (3GPP) long term evolution(LTE) system, the PHICH is repeatedly transmitted three times in orderto obtain diversity gain. Through how many OFDM symbols the PHICH istransmitted is determined depending on information transmitted through aprimary broadcast channel (PBCH) and on whether or not a subframe is formulticast broadcast over single frequency network (MBSFN). If the PHICHis transmitted through one OFDM symbol, the PHICH repeating three timesshould be evenly distributed over a frequency bandwidth of one OFDMsymbol. If the PHICH is transmitted through three OFDM symbols, eachrepetition is mapped to a corresponding OFDM symbol.

FIGS. 2 and 3 illustrate resource element groups (REGs) to which thePHICH is mapped.

Each REG is comprised of four resource elements. Since a first OFDMsymbol includes reference signals RS0 and RS1, locations except for thereference signal locations are available for the resource elements. InFIG. 3, even a second OFDM symbol includes reference signals RS2 andRS3.

FIGS. 4 and 5 illustrate examples of mapping a PHICH when a spreadingfactor (SF) is 4. When an SF is 4, one repetition of one PHICH group ismapped to one REG.

In FIGS. 4 and 5, precoding for transmit diversity is applied. A₁₁, A₂₁,A₃₁, and A₄₁ denote resource elements of an REG constituting a specificPHICH. C₁, C₂, C₃, and C₄ denote resource elements of an REG for PCHICHor a physical downlink control channel (PDCCH). FIGS. 4 and 5 correspondto the cases where the number of antennas is 1 and 2, respectively, whenreference signals are not considered.

FIGS. 6 and 7 illustrate examples of mapping a PHICH when an SF is 2.When an SF is 2, one repetition of two PHICH groups is mapped to oneREG.

Precoding for transmit diversity is applied to FIGS. 6 and 7. FIGS. 6and 7 correspond to the cases where the number of antennas is 1 and 2,respectively, when reference signals are not considered.

In actual implementation as illustrated in FIGS. 2 and 3, it should beconsidered that the number of available REGs in an OFDM symbol includingreference signals is not equal to the number of available REGs in anOFDM symbol which does not include reference signals.

Meanwhile, if a sequence for mapping the PHICH is denoted as y^((p))(0), K, y ^((p))(M_(symb)−1), then y ^((p))(n) satisfies y^((p))=Σy_(i) ^((p))(n), which indicates the sum of all PHICHs in onePHICH group. y_(i) ^((P))(n) denotes an i-th PHICH in a specific PHICHgroup. In this case, z^((p))(i)=

y^((p))(4i),y^((p))(4i+1), y^((p))(4i+2), y^((p))(4i+3)

(where i=0, 1, 2) denotes a symbol quadruplet for an antenna port p.

An index of a PHICH group has m′=0 as an initial value. A symbolquadruplet z^((p))(i) at m′ is mapped to an REG of (k′, l′)_(i) (wherel′_(i) is an index of an OFDM symbol in which i-th repetition of a PHICHgroup is transmitted, and k′_(i) is an index of a frequency domain).

When a PHICH is transmitted through two OFDM symbols, the PHICH isrepeated twice upon a first OFDM symbol and repeated once upon a secondOFDM symbol according to a transmitted PHICH group. Conversely, thePHICH may be repeated once upon the first OFDM symbol and repeated twiceupon the second OFDM symbol. This may be expressed by the followingEquation 1.

$\begin{matrix}{l_{i}^{\prime} = \left\{ \begin{matrix}0 & \begin{matrix}{{{normal}\mspace{14mu} {PHICH}\mspace{14mu} {duration}},} \\{{all}\mspace{14mu} {subframes}}\end{matrix} \\i & \begin{matrix}{{{extended}\mspace{14mu} {PHICH}\mspace{14mu} {duration}},} \\{{non}\text{-}{MBSFN}\mspace{14mu} {subframes}}\end{matrix} \\{\left( {\left\lfloor {m^{\prime}/2} \right\rfloor + i + 1} \right){mod}\; 2} & \begin{matrix}{{{extended}\mspace{14mu} {PHICH}\mspace{14mu} {duration}},} \\{{MBSFN}\mspace{14mu} {subframes}}\end{matrix}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

In Equation 1, l′_(i) denotes an index of an OFDM symbol in which i-threpetition of a PHICH group is transmitted, m′ denotes an index of aPHICH group, and i denotes the number of repetitions of a PHICH. Whenthe PHICH is repeated three times, i has values of 0, 1, and 2.

FIGS. 8 to 10 illustratively show Equation 1.

FIGS. 8 and 9 show the cases where l′_(i)=0 and l′_(i)=(└′/2┘+i+1)mod 2,respectively. FIG. 10 shows the case where l′_(i)=i and a PHICH group isrepeated at a PHICH duration of 3.

A PHICH, which is an important channel for transmitting ACK/NACK signalsindicating whether or not data has been received, should be transmittedas stably as possible. Further, since ACK/NACK signals should betransmitted to a user even in a cell edge, substantial power is usedcompared with other channels. If locations for transmitting the PHICHsin respective cells are the same, PHICH transmission performance may bedeteriorated due to interference caused by transmission of the PHICHbetween neighbor cells. Accordingly, if transmission locations of thePHICH in respective cells differ, interference caused by transmission ofthe PHICH between neighbor cells is reduced. Consequently, PHICHtransmission performance can be improved. Namely, if mapping locationsof the PHICH are determined according to cell IDs, the above-describedproblem can be solved. The PHICH is repeatedly transmitted three timesto obtain diversity gain. To increase the diversity gain, eachrepetition should be evenly distributed over an entire frequencybandwidth.

To satisfy the above conditions, a PHICH group is transmitted in unitsof an REG consisting of 4 resource elements. The location of atransmission start REG of the PHICH is designated according to a cell IDand each repetition of the PHICH is arranged at an interval of a valueobtained by dividing the number of REGs which can be transmitted by 3based on the transmission start REG. However, when such a repetition ofthe PHICH is distributed over a plurality of OFDM symbols, the number ofREGs which can be used for PHICH transmission in each OFDM symboldiffers. That is because, in the first OFDM symbol, a physical controlformat indicator channel (PCFICH) for transmitting information includingthe number of OFDM symbols used for a control channel is transmitted,and because reference signals transmitted in the first and second OFDMsymbols differ according to the number of transmit antennas. When thePHICH is transmitted through multiple OFDM symbols including differentREGs, since the number of REGs in each OFDM symbol differs, repetitionsof each PHICH are not evenly dispersed over an entire frequencybandwidth. The location of the first REG should be designated accordingto a cell ID and a repetitive pattern should be allocated at regularintervals based on an index of the first REG. However, since resolutionof a frequency location depending on the index differs according to thenumber of REGs in each OFDM symbol, there exists a defect that areference location is changed.

Therefore, when the PHICH is transmitted through multiple OFDM symbols,if the start location according to the cell ID is determined inconsideration of a ratio of REGs of the first start symbol to REGs ofthe other symbols, the above problem can be solved. When the PHICH istransmitted through one or three OFDM symbols, the location of the firststart symbol is always the first OFDM symbol. However, when the PHICH istransmitted through two OFDM symbols, the first PHICH group is startedfrom the second OFDM symbol. Accordingly, if the ratio of REGs isconsidered, a reference symbol should be changed.

The above description may be expressed by the following equation 2.

$\begin{matrix}{{\overset{\_}{n}}_{i} = \left\{ \begin{matrix}{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{0}^{\prime}}} \right) \right\rfloor + m^{\prime}} \right)\mspace{14mu} {mod}\mspace{14mu} n_{l_{i}^{\prime}}^{\prime}},} & {i = 0} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{0}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {n_{l_{i}^{\prime}}^{\prime}/3} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 1} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{0}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {2\; {n_{l_{i}^{\prime}}^{\prime}/3}} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 2}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 2} \right\rbrack\end{matrix}$

In Equation 2, n _(i) denotes an index of an REG in which a repetitivepattern of each PHICH is transmitted, N_(ID) ^(cell) denotes a cell ID,n′_(l′) _(i) denotes the number of REGs which can be used for PHICHtransmission in an OFDM symbol l′_(i), n′_(l′) _(i) /n′₀ denotes a ratiobetween the number of available resource element groups in an OFDMsymbol l′_(i) and the number of available resource element groups in afirst OFDM symbol and is a parameter for solving a problem caused by thedifferent number of REGs between symbols, and m′ denotes an index of aPHICH group as indicated in Equation 1. m′ is desirably increased by 1.

FIG. 11 illustrates an example of a PHICH mapping method according to anexemplary embodiment of the present invention. As illustrated in FIG.11, PHICH resource collision can be avoided based on cell planning.

If the PHICH is mapped from the second OFDM symbol, n′_(l′) _(i) /n′₀ ischanged to n′_(l′) _(i) /n′₁. This may be expressed by the followingEquation 3.

$\begin{matrix}{{\overset{\_}{n}}_{i} = \left\{ \begin{matrix}{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{1}^{\prime}}} \right) \right\rfloor + m^{\prime}} \right)\mspace{14mu} {mod}\mspace{14mu} n_{l_{i}^{\prime}}^{\prime}},} & {i = 0} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{1}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {n_{l_{i}^{\prime}}^{\prime}/3} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 1} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{1}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {2\; {n_{l_{i}^{\prime}}^{\prime}/3}} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 2}\end{matrix} \right.} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

In Equation 3, N_(ID) ^(cell) denotes a cell ID, i denotes an index of arepetitive pattern, n′_(l′) _(i) /n′₁ denotes a ratio between the numberof available resource element groups in an OFDM symbol l′_(i) and thenumber of available resource element groups in a second OFDM symbol, andm′ denotes an index of a PHICH group. As in Equation 2, m′ is desirablyincreased by 1.

Meanwhile, the location of the first PHICH group is allocated and thenthe other PHICH groups may be mapped successively after the first PHICHgroup.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present inventionwithout departing from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

The present invention provides a mapping method for frequency and OFDMsymbol regions of a signal transmitted on downlink in a cellular OFDMwireless packet communication system and may be applied to a 3GPP LTEsystem, etc.

Text Proposal disclosed in pages 6-7 of U.S. Provisional ApplicationSer. No. 61/029,895 and previously incorporated by reference into U.S.patent application Ser. Nos. 12/388,243 and 13/012,702.

6.9.3 Mapping to Resource Elements

The sequence y ^((p))(0), . . . , y ^((p))(M_(symb)−1) is defined by

y ^((p))(n)=Σy _(i) ^((p))(n)

where the sum is over all PHICHs in a PHICH group and y_(i) ^((P))(n)represents the symbol sequence from the i:th PHICH in the PHICH group.Let z^((p))(i)=

y^((p))(4i),y^((p))(4i+1),y^((p))(4i+2),y^((p))(4i+3)

, i=0, 1, 2 denote symbol quadruplet i for antenna port p.Mapping to resource elements is defined in terms of symbol quadrupletsaccording to steps 1-9 below:1) Initialize m′=0 (PHICH group number)2) For each value of i=0, 1, 23) Symbol-quadruplet z^((p))(i) from PHICH group m′ is mapped to theresource-element group represented by (k′, l′)_(i) as defined in Section6.2.4 where the indices k′_(i) and l′_(i) are given by steps 4-7 below:4) The time-domain l′_(i) is given by

$l_{i}^{\prime} = \left\{ \begin{matrix}0 & \begin{matrix}{{{normal}\mspace{14mu} {PHICH}\mspace{14mu} {duration}},} \\{{all}\mspace{14mu} {subframes}}\end{matrix} \\i & \begin{matrix}{{{extended}\mspace{14mu} {PHICH}\mspace{14mu} {duration}},} \\{{non}\text{-}{MBSFN}\mspace{14mu} {subframes}}\end{matrix} \\{\left( {\left\lfloor {m^{\prime}/2} \right\rfloor + i + 1} \right){mod}\; 2} & \begin{matrix}{{{extended}\mspace{14mu} {PHICH}\mspace{14mu} {duration}},} \\{{MBSFN}\mspace{14mu} {subframes}}\end{matrix}\end{matrix} \right.$

5) Let n′_(l′) _(i) denote the number of resource element groups notassigned to PCFICH in OFDM symbol l′_(i;)6) Number the resource-element groups not assigned to PCFICH in OFDMsymbol l′_(i) from 0 to n′_(l′) _(i) −1, starting from theresource-element group with the lowest frequency-domain index.7) Set the frequency-domain index k′_(i) to the resource-element groupassigned the number n _(ti), where n _(i) is given by

${\overset{\_}{n}}_{i} = \left\{ \begin{matrix}{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{0}^{\prime}}} \right) \right\rfloor + m^{\prime}} \right)\mspace{14mu} {mod}\mspace{14mu} n_{l_{i}^{\prime}}^{\prime}},} & {i = 0} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{0}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {n_{l_{i}^{\prime}}^{\prime}/3} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 1} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{0}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {2\; {n_{l_{i}^{\prime}}^{\prime}/3}} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 2}\end{matrix} \right.$

if normal PHICH duration in all subframes or extended PHICH duration inMBSFN subframes, and by

${\overset{\_}{n}}_{i} = \left\{ \begin{matrix}{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{1}^{\prime}}} \right) \right\rfloor + m^{\prime}} \right)\mspace{14mu} {mod}\mspace{14mu} n_{l_{i}^{\prime}}^{\prime}},} & {i = 0} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{1}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {n_{l_{i}^{\prime}}^{\prime}/3} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 1} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{1}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {2\; {n_{l_{i}^{\prime}}^{\prime}/3}} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 2}\end{matrix} \right.$

otherwise.8) Increase m′ by 1.9) Repeat from step 2 until all PHICH groups have been assigned.

What is claimed is:
 1. A method for determining acknowledgement/negativeacknowledgement (ACK/NACK) mapped in at least two orthogonal frequencydivision multiplexing (OFDM) symbols, the method comprising: receiving asignal comprising the ACK/NACK; determining an index of a first resourceelement group (REG) in a first OFDM symbol based on a first ratiocalculated using a number of available resource element groups (REGs) inthe first OFDM symbol and a number of available REGs in a second OFDMsymbol, the index of the first REG corresponding to a frequency domainlocation; and determining the ACK/NACK from the signal according to thedetermined index of the first REG, wherein available REGs are REGs notassigned to Physical Control Format Indicator Channel (PCFICH).
 2. Themethod of claim 1, wherein an index of the first OFDM symbol correspondsto an OFDM symbol index l′=0, and an index of the second OFDM symbolcorresponds to an OFDM symbol index l′=1.
 3. The method of claim 2,wherein the first ratio is calculated as the number of available REGs inthe first OFDM symbol to the number of available REGs in the second OFDMsymbol.
 4. The method of claim 2, further comprising: determining theACK/NACK from the signal based on a second REG in the second OFDM symboland a third REG in the second OFDM symbol.
 5. The method of claim 4,wherein an index ( n _(i)) of an i-th REG to which the ACK/NACK ismapped is determined using the following equation:${\overset{\_}{n}}_{i} = \left\{ \begin{matrix}{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{1}^{\prime}}} \right) \right\rfloor + m^{\prime}} \right)\mspace{14mu} {mod}\mspace{14mu} n_{l_{i}^{\prime}}^{\prime}},} & {i = 0} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{1}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {n_{l_{i}^{\prime}}^{\prime}/3} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 1} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{1}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {2\; {n_{l_{i}^{\prime}}^{\prime}/3}} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 2}\end{matrix} \right.$ where an index of the second REG in the secondOFDM symbol corresponds to the index ( n ₀) of the i-th REG when i=0,the index of the first REG in the first OFDM symbol corresponds to theindex ( n ₁) of the i-th REG when i=1, an index of the third REG in thesecond OFDM symbol corresponds to the index ( n ₂) of the i-th REG wheni=2, N_(ID) ^(cell) denotes a cell ID, l′_(i) denotes an index of anOFDM symbol comprising the i-th REG when i=0, 1, or 2, n′_(l′) _(i)denotes a number of available REGs in an OFDM symbol having an indexl′_(i), n′₁ denotes a number of available REGs in an OFDM symbol havingan index l′=1, and m′ is determined based on an index of a physicalhybrid automatic repeat request indicator channel (PHICH) group.
 6. Themethod of claim 2, further comprising: determining the ACK/NACK from thesignal based on a second REG in the first OFDM symbol and a third REG inthe second OFDM symbol.
 7. The method of claim 6, wherein an index ( n_(i)) of an i-th REG to which the ACK/NACK is mapped is determined usingthe following equation: ${\overset{\_}{n}}_{i} = \left\{ \begin{matrix}{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{1}^{\prime}}} \right) \right\rfloor + m^{\prime}} \right)\mspace{14mu} {mod}\mspace{14mu} n_{l_{i}^{\prime}}^{\prime}},} & {i = 0} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{1}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {n_{l_{i}^{\prime}}^{\prime}/3} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 1} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{1}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {2\; {n_{l_{i}^{\prime}}^{\prime}/3}} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 2}\end{matrix} \right.$ where the index of the first REG in the first OFDMsymbol corresponds to the index ( n ₀) of the i-th REG when i=0, anindex of the third REG in the second OFDM symbol corresponds to theindex ( n ₁) of the i-th REG when i=1, an index of the second REG in thefirst OFDM symbol corresponds to the index ( n ₂) of the i-th REG wheni=2, N_(ID) ^(cell) denotes a cell ID, l′_(i) denotes an index of anOFDM symbol comprising the i-th REG when i=0, 1, or 2, n′_(l′) _(i)denotes a number of available REGs in an OFDM symbol having an indexl′_(i), n′₁ denotes a number of available REGs in an OFDM symbol havingan index l′=1, and m′ is determined based on an index of a physicalhybrid automatic repeat request indicator channel (PHICH) group.
 8. Themethod of claim 1, wherein an index of the first OFDM symbol correspondsto an OFDM symbol index l′=1, and an index of the second OFDM symbolcorresponds to an OFDM symbol index l′=0.
 9. The method of claim 8,further comprising: determining the ACK/NACK from the signal accordingto an index of a second REG in the second OFDM symbol; determining anindex of a third REG in a third OFDM symbol based on a second ratiocalculated using the number of available REGs in the second OFDM symboland a number of available REGs in the third OFDM symbol; and determiningthe ACK/NACK from the signal according to the determined index of thethird REG.
 10. The method of claim 9, wherein the first ratio iscalculated as the number of available REGs in the first OFDM symbol tothe number of available REGs in the second OFDM symbol, and the secondratio is calculated as the number of available REGs in the third OFDMsymbol to the number of available REGs in the second OFDM symbol. 11.The method of claim 9, wherein an index ( n _(i)) of an i-th REG towhich the ACK/NACK is mapped is determined using the following equation:${\overset{\_}{n}}_{i} = \left\{ \begin{matrix}{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{0}^{\prime}}} \right) \right\rfloor + m^{\prime}} \right)\mspace{14mu} {mod}\mspace{14mu} n_{l_{i}^{\prime}}^{\prime}},} & {i = 0} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{0}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {n_{l_{i}^{\prime}}^{\prime}/3} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 1} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{0}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {2\; {n_{l_{i}^{\prime}}^{\prime}/3}} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 2}\end{matrix} \right.$ where the index of the second REG in the secondOFDM symbol corresponds to the index ( n ₀) of the i-th REG when i=0,the index of the first REG in the first OFDM symbol corresponds to theindex ( n ₁) of the i-th REG when i=1, the index of the third REG in thethird OFDM symbol corresponds to the index ( n ₂) of the i-th REG wheni=2, N_(ID) ^(cell) denotes a cell ID, l′_(i) denotes an index of anOFDM symbol comprising the i-th REG when i=0, 1, or 2, n′_(l′) _(i)denotes a number of available REGs in an OFDM symbol having an indexl′_(i), n′₀ denotes a number of available REGs in an OFDM symbol havingan index l′=0, and m′ is determined based on an index of a physicalhybrid automatic repeat request indicator channel (PHICH) group.
 12. Themethod of claim 1, wherein the number of available REGs in the firstOFDM symbol is defined as a number of REGs not assigned to PCFICH in thefirst OFDM symbol, and the number of available REGs in the second OFDMsymbol is defined as a number of REGs not assigned to PCFICH in thesecond OFDM symbol.
 13. An apparatus to determineacknowledgement/negative acknowledgement (ACK/NACK) mapped in at leasttwo orthogonal frequency division multiplexing (OFDM) symbols, theapparatus comprising: a receiver to receive a signal comprising theACK/NACK; and a processor configured to determine an index of a firstresource element group (REG) in a first OFDM symbol based on a firstratio calculated using a number of available resource element groups(REGs) in the first OFDM symbol and a number of available REGs in asecond OFDM symbol, and to determine the ACK/NACK from the signalaccording to the determined index of the first REG, the index of thefirst REG corresponding to a frequency domain location.
 14. Theapparatus of claim 13, wherein the number of available REGs in the firstOFDM symbol is defined as a number of REGs not assigned to PhysicalControl Format Indicator Channel (PCFICH) in the first OFDM symbol, andthe number of available REGs in the second OFDM symbol is defined as anumber of REGs not assigned to PCFICH in the second OFDM symbol.
 15. Theapparatus of claim 13, wherein an index of the first OFDM symbolcorresponds to an OFDM symbol index l′=0, and an index of the secondOFDM symbol corresponds to an OFDM symbol index l′=1, and wherein theprocessor is configured to determine the ACK/NACK from the signal basedon a second REG in the second OFDM symbol and a third REG in the secondOFDM symbol.
 16. The apparatus of claim 15, wherein an index ( n _(i))of an i-th REG to which the ACK/NACK is mapped is determined using thefollowing equation: ${\overset{\_}{n}}_{i} = \left\{ \begin{matrix}{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{1}^{\prime}}} \right) \right\rfloor + m^{\prime}} \right)\mspace{14mu} {mod}\mspace{14mu} n_{l_{i}^{\prime}}^{\prime}},} & {i = 0} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{1}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {n_{l_{i}^{\prime}}^{\prime}/3} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 1} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{1}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {2\; {n_{l_{i}^{\prime}}^{\prime}/3}} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 2}\end{matrix} \right.$ where an index of the second REG in the secondOFDM symbol corresponds to the index ( n _(o)) of the i-th REG when i=0,the index of the first REG in the first OFDM symbol corresponds to theindex ( n ₁) of the i-th REG when i=1, an index of the third REG in thesecond OFDM symbol corresponds to the index ( n ₂) of the i-th REG wheni=2, N_(ID) ^(cell) denotes a ell ID, l′_(i) denotes an index of an OFDMsymbol comprising the i-th REG when i=0, 1, or 2, n′_(l′) _(i) denotes anumber of available REGs in an OFDM symbol having an index l′_(i),n′_(i) denotes a number of available REGs in an OFDM symbol having anindex l′=1, and m′ is determined based on an index of a physical hybridautomatic repeat request indicator channel (PHICH) group.
 17. Theapparatus of claim 13, wherein an index of the first OFDM symbolcorresponds to an OFDM symbol index l′=0, and an index of the secondOFDM symbol corresponds to an OFDM symbol index l′=1, and wherein theprocessor is configured to determine the ACK/NACK from the signal basedon a second REG in the first OFDM symbol and a third REG in the secondOFDM symbol.
 18. The apparatus of claim 17, wherein an index ( nn_(i))of an i-th REG to which the ACK/NACK is mapped is determined using thefollowing equation: ${\overset{\_}{n}}_{i} = \left\{ \begin{matrix}{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{1}^{\prime}}} \right) \right\rfloor + m^{\prime}} \right)\mspace{14mu} {mod}\mspace{14mu} n_{l_{i}^{\prime}}^{\prime}},} & {i = 0} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{1}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {n_{l_{i}^{\prime}}^{\prime}/3} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 1} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{1}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {2\; {n_{l_{i}^{\prime}}^{\prime}/3}} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 2}\end{matrix} \right.$ where the index of the first REG in the first OFDMsymbol corresponds to the index ( n ₀) of the i-th REG when i=0, anindex of the third REG in the second OFDM symbol corresponds to theindex ( n ₁) of the i-th REG when i=1, an index of the second REG in thefirst OFDM symbol corresponds to the index ( n ₂) of the i-th REG wheni=2, N_(ID) ^(cell) denotes a cell ID, l′_(i) denotes an index of anOFDM symbol comprising the i-th REG when i=0, 1, or 2, n′_(l′) _(i)denotes a number of available REGs in an OFDM symbol having an indexl′_(i), n′₁ denotes a number of available REGs in an OFDM symbol havingan index l′=1, and m′ is determined based on an index of a physicalhybrid automatic repeat request indicator channel (PHICH) group.
 19. Theapparatus of claim 13, wherein an index of the first OFDM symbolcorresponds to an OFDM symbol index l′=1, and an index of the secondOFDM symbol corresponds to an OFDM symbol index l′=0, wherein theprocessor is configured to determine the ACK/NACK from the signal basedon a second REG in the second OFDM symbol, to determine an index of athird REG in a third OFDM symbol based on a second ratio calculatedusing the number of available REGs in the second OFDM symbol and anumber of available REGs in the third OFDM symbol, and to determine theACK/NACK from the signal according to the determined index of the thirdREG, and wherein an index ( n _(i)) of an i-th REG to which the ACK/NACKis mapped is determined using the following equation:${\overset{\_}{n}}_{i} = \left\{ \begin{matrix}{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{0}^{\prime}}} \right) \right\rfloor + m^{\prime}} \right)\mspace{14mu} {mod}\mspace{14mu} n_{l_{i}^{\prime}}^{\prime}},} & {i = 0} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{0}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {n_{l_{i}^{\prime}}^{\prime}/3} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 1} \\{{\left( {\left\lfloor \left( {N_{ID}^{cell} \cdot {n_{l_{i}^{\prime}}^{\prime}/n_{0}^{\prime}}} \right) \right\rfloor + m^{\prime} + \left\lfloor {2\; {n_{l_{i}^{\prime}}^{\prime}/3}} \right\rfloor} \right)\mspace{14mu} {mod}{\mspace{11mu} \;}n_{l_{i}^{\prime}}^{\prime}},} & {i = 2}\end{matrix} \right.$ where an index of the second REG in the secondOFDM symbol corresponds to the index ( n ₀) of the i-th REG when i=0,the index of the first REG in the first OFDM symbol corresponds to theindex ( n ₁) of the i-th REG when i=1, the index of the third REG in thethird OFDM symbol corresponds to the index ( n ₂) of the i-th REG wheni=2, N_(ID) ^(cell) denotes a cell ID, l′_(i) denotes an index of anOFDM symbol comprising the i-th REG when i=0, 1, or 2, n′_(l′) _(i)denotes a number of available REGs in an OFDM symbol having an indexl′_(i), n′₀ denotes a number of available REGs in an OFDM symbol havingan index l′=0, and m′ is determined based on an index of a physicalhybrid automatic repeat request indicator channel (PHICH) group.
 20. Amethod for determining acknowledgement/negative acknowledgement(ACK/NACK) mapped in at least two orthogonal frequency divisionmultiplexing (OFDM) symbols, the method comprising: receiving a signalcomprising the ACK/NACK; determining an index of a first resourceelement group (REG) in a first OFDM symbol based on a first ratiocalculated using a number of available resource element groups (REGs) inthe first OFDM symbol and a number of available REGs in a second OFDMsymbol, the index of the first REG corresponding to a frequency domainlocation; determining the ACK/NACK from the signal according to thedetermined index of the first REG; and determining the ACK/NACK from thesignal based on a second REG in the second OFDM symbol and a third REG,the third REG being included in the first OFDM symbol, the second OFDMsymbol, or a third OFDM symbol, wherein a number of available REGs in anOFDM symbol is defined as a number of REGs not assigned to PhysicalControl Format Indicator Channel (PCFICH) in an OFDM symbol.